1. Field of the Invention
The present invention relates to a lubricating oil composition for internal combustion engines. Specifically, the present invention relates to a lubricating oil composition for internal combustion engines which is a lubricating oil composition for internal combustion engines of passenger and commercial four-wheeled vehicles and includes a base oil having a low viscosity and a specific complex polyester mixture.
2. Description of the Related Art
In general, a lubricating oil composition for internal combustion engines includes a base oil and various additives. As the base oil, mineral oils to be obtained from crude oil, and ester-based oils, fluorine oils, poly-α-olefin-based oils and the like to be chemically synthesized are generally used.
There are many quality standards for a lubricating oil composition used for internal combustion engines of vehicles such as four-wheeled vehicles from the viewpoint of durability and environmental protection. Among these, in the quality standards of gasoline engine oils for vehicles established by International Lubricants Standardization and Approval Committee (ILSAC), in consideration of influences on engine components, various oil standards are established. Among these, regarding wear resistance reliability, there is an item which restricts design of engine components and a base oil which does not meet the standards regarding wear resistance reliability cannot be used as a base oil of a lubricating oil composition for internal combustion engines of vehicles and the like.
In recent years, there has been a problem of improving fuel efficiency of vehicles from the viewpoint of environmental protection. In order to improve fuel efficiency of vehicles, there is a method of improving the fuel efficiency performance of an engine oil. In order to improve the fuel efficiency performance of an engine oil, it is important to lower the viscosity of the base oil. However, in the case of lowering the viscosity of the base oil, there may be an adverse influence on boundary lubrication and wear may be accelerated. Therefore, in order to prevent wear, it has been considered to add various load resistant additives such as an oily agent, an anti-wear agent and an extreme pressure additive. For example, in WO2011/007643A and JP2013-060533A, it is proposed that high wear resistance can be exhibited by adding an additive such as an organic metal compound to a base oil.